The invention is related to a process for the catalytic dewaxing of a hydrocarbon oil feed including waxy molecules and more than 500 ppmw of sulphur or sulphur containing compounds with a catalyst composition comprising at least a binder, aluminosilicate zeolite crystallites and a Group VIII metal. The invention is especially directed to a process to prepare a low pour point lubricating base oil stock or a middle distillate having both a low pour point and cloud point.
It is well known that catalysts comprising alumino-silicate zeolite crystallites will deactivate when used in a process for the catalytic dewaxing of a hydrocarbon oil feed in the presence of high amounts of sulphur. For example in U.S. Pat. No. 5,723,716 it is stated that waxy feeds secured from natural petroleum sources will contain quantities of sulphur and nitrogen compounds which are known to deactivate wax hydroisomerisation catalysts. Exemplary catalysts described in this patent publication comprised palladium on zeolites having the TON topology. According to this patent specification this deactivation is prevented by using a feed containing no more than 10 ppm sulphur and no more than 2 ppm nitrogen.
WO-A-9801515 describes the dewaxing of an oil feed having a sulphur content of 45 ppmw and a nitrogen content of 1 ppmw using a dewaxing catalyst comprising 0.8% w platinum supported on a carrier consisting of surface dealuminated ZSM-5 having a silica to alumina molar ratio of 51.6 and a silica binder (70% w surface dealuminated ZSM-5 and 30% w silica binder). According to this patent publication these low levels of sulphur and nitrogen in the dewaxing feedstock are needed because sulphur and nitrogen are known to poison the noble metal-based dewaxing catalyst. According to this patent publication the sulphur and nitrogen contents are decreased in the oil feed by first hydrocracking, also referred to as hydrotreating, the feed and subsequently separating a sulphur and nitrogen rich gaseous fraction from the liquid hydrocracker effluent.
U.S. Pat. No. 4,797,266 describes in their examples a catalytic dewaxing process of a hydrocarbon oil feed containing 29 ppmw of nitrogen compounds and 2800 ppmw of sulphur compounds by using a combined ZSM-5/ferrierite/palladium containing catalyst. In order to maintain a constant pour point reduction the reaction temperature had to be raised by 1.9° F. per day due to catalyst activity decline. According to this publication the temperature raise in case a ZSM-5/palladium catalyst was used was 6.3° F. per day.
WO-A-9641849 describes a dewaxing catalyst composition comprising palladium and/or platinum, an aluminosilicate zeolite crystallites having medium pore size, a diameter in the range of from 0.35 to 0.80 nm, and a low acidity refractory oxide binder material which is essentially free of alumina, wherein the surface of the aluminosilicate zeolite crystallites has been modified by subjecting the aluminosilicate zeolite crystallites to a surface dealumination treatment. No indication is given in this publication that such a catalyst would be stable when using a feed with a high content of sulphur and nitrogen.
EP-A-180354 describes the simultaneous catalytic dewaxing, denitrogenation and desulphurization of a vacuum gas oil by making use of a catalyst composition consisting of nickel, molybdenum, and zeolite beta and an alumina binder. A disadvantage of simultaneous dewaxing and hydrotreating is the lack of flexibility between both modes of operation. For example in winter you may require more dewaxing, to achieve good cold flow properties, while in summer only hydrotreating activity is desired.
The object of this invention is a dewaxing process in which the decline in catalyst activity is less severe as in the process of U.S. Pat. No. 4,797,266 when a hydrocarbon oil feed is used containing higher levels of sulphur compounds.